In recent years, frequency equalization single-carrier transmission systems have been studied with an eye toward next-generation mobile communication systems. In the frequency equalization single-carrier transmission system, data symbols arranged in the time domain are transmitted by a single carrier. A receiving apparatus corrects signal distortion in the transmission path by equalizing that distortion on the frequency axis. More specifically, the receiving apparatus calculates a channel estimation value for each frequency on the frequency domain, and performs weighting for equalizing channel distortion on a frequency-by-frequency basis. Then the received data is demodulated.
The art disclosed in Patent Document 1 relates to the above frequency equalization single-carrier transmission systems. This art will be briefly described below. As shown in FIG. 1, the transmission system disclosed in Patent Document 1 generates signals in which a predetermined portion of the rear part of transmission data (data part in the drawing) is attached to the head of the data part as a guard interval (hereinafter abbreviated as “GI”). The signals generated are then transmitted from the transmitting apparatus, and signals combining direct waves and delayed waves arrive at the receiving apparatus. At the receiving apparatus, as shown in FIG. 2, a timing synchronization process is performed for the received data, and signals of the length of the data part are extracted from the beginning of the data part of the direct wave. The extracted signals thereby include the direct wave component, the delayed wave component and the noise component from the receiving apparatus, and the extracted signals combine all of these components. Then, the extracted signals are subjected to signal distortion correction process in the frequency domain (frequency domain equalization) and demodulated.
A GI is also called a cyclic prefix (“CP”).    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-349889